(1) The glnD gene which encodes uridylytransferase-uridylyl-removing enzyme (UT-UR) in E. coli was cloned into a plasmid vector carrying the strong regulatable Lambda phage promoter pL such that UR-UR was overproduced to the levels approaching 800-fold. Induction of this enzyme was optimized by varying the induction temperature and the growth medium. Detailed restriction maps and the transcriptional direction of the glnD gene were also established. (2) The promoter region of the glnD gene was inserted into a promoter expression vector and its transcriptional control was studied by measuring galactokinase transcribed from this promoter. The result indicates that the glnD gene is metabolically regulated. (3) The glnE gene (structural gene for adenylyltransferase in E. coli) was subcloned into pBR322 and subsequently into the pL vector. Nearly 300- to 400-fold amplification in the synthesis of adenylyltransferase was achieved. (4) Crude extracts of Saccharomyces cerevisiae were separated into two peaks containing glutamine synthetase with different catalytic properties. Glutamine synthetase in the earlier peak exhibited a higher ratio of biosynthetic to (nonphysiological) transferase activity than that in the latter peak, and the ratio difference became more pronounced upon aging. The glutamine synthetase of higher biosynthetic activity was purified to apparent homogeneity.